Natural graphite-reinforced cyclized butadiene elastomers

ABSTRACT

Natural graphite-reinforced, cyclized butadiene elastomers are prepared by mixing a homopolymer or copolymer of butadiene and a monoolefinic monomer with natural graphite, curing this mixture with an organic peroxide or mononuclear quinone and thereafter cyclizing the cured mixture by heating at a temperature of 350*700*F. The natural graphite-reinforced, cyclized butadiene polymers are hard, infusible, thermoset materials which have outstanding physical properties, particularly modulii, and resistance to air oxidation, inorganic acids and other chemicals, and overall aging at elevated temperatures.

United States Patent Vanderbilt [451 Feb. 18,1975

[ NATURAL GRAPHITE-REINFORCED CYCLIZED BUTADIENE ELASTOMERS [76]Inventor: Byron M. Vanderbilt, 516 Lake Shore Ln., Chapel Hill, NC.27154 [22] Filed: Dec. 22, 1972 [21] Appl. No.: 317,612

[52] U.S. Cl 260/4232, 260/4215, 260/833, 260/85.l, 260/947 A [51] Int.Cl C081? 11/18, C08d ll/00 [58] Field of Search 260/734, 85.1, 94.7 A,260/947 HA, 94.7 N, 83.3, 42.32, 42.15

[56] References Cited UNITED STATES PATENTS 2,625,523 [/1953 Garher ctal 260/890 3,274,148 9/1966 Sparks ct a1. 260/851 OTHER PUBLICATIONSRubber World-Materials & Compounding Ingredients for Rubber & Plastics(Rubber World) (N.Y.) (1965), page 443, TS 1890153.

Primary Examiner-Melvyn l. Marquis Assistant Examiner-H. H. FletcherAttorney, Agent, or Firm-Mills and Coats [57] ABSTRACT Naturalgraphite-reinforced, cyclized butadiene elastomers are prepared bymixing a homopolymer or copolymer of butadiene and a monoolefinicmonomer with natural graphite, curing this mixture with an 0rganicperoxide or mononuclear quinone and thereafter cyclizing the curedmixture by heating at a temperature of 350-700F. The naturalgraphite-reinforced, cyclized butadiene polymers are hard, infusible,thermoset materials which have outstanding physical properties,particularly modulii, and resistance to air oxidation, inorganic acidsand other chemicals, and overall aging at elevated temperatures.

8 Claims, N0 Drawings NATURAL GRAPHITE-REINFORCED CYCLIZED BUTADIENEELASTOMERS BACKGROUND OF THE INVENTION As is well known, the use offillers in elastomers, particularly carbon blacks, results invulcanizates of greatly improved properties. For example, whereas curedpure gum SBR is of low strength, very low abrasion resistance, and poortear resistance, that containing 50 parts or so of carbon black per I ofSBR makes a tough, long-serviceable tire tread. In case of plastics, useof carbon blacks in concentrations higher than a very few. parts tendsto degrade physical properties rather than to enhance them. Graphitefillers have only very limited use in elastomers and practically nocommerical utilization in plastics.

It has now been found that by proper choice of graphite filler inselected butadiene polymers and copolymers, it is possible byvulcanization followed by thermal cyclization to produce thermosetplastics containing as high as 85 percent graphite by weight and havingstrengths and modulii greater than those of the corresponding gumstocks. Due to the combination of high physical strength and stiffnessalong with high graphite content, such composites are particularlysuitable for constructing equipment to handle corrosive chemicals, asbearings requiring no lubricants, and for uses where moderate electricalconductivity is required.

SUMMARY OF THE INVENTION This invention relates to cyclized butadieneelastomers. Butadiene homopolymers and copolymers of butadiene with amonoolefinic monomer are compounded with natural graphite and cured withan organic peroxide or mononuclear quinone. The product is thereaftercyclized by heating at a temperature of about 350-700F.

The resulting cyclized butadiene polymers are hard infusible thermosetcompositions with outstanding physical properties.

PROCESS OF THE INVENTION The Elastomeric Butadiene Polymer Elastomericbutadiene polymers employed in the process of this invention are thosewhich have at least mole percent, preferably at least mole percent, oftheir unsaturation present as the 1,2-type. For the purposes of thepresent invention, the term butadiene polymer" encompasseshomopolybutadiene and c0- polymers of butadiene and at least one otherolefinically unsaturated monomer. Piperylene may also be used forpreparing such elastomers, but those of butadiene are preferred. Theterm monomer as used in the specification and claims means olefinicallyunsaturated monomers having only one site of unsaturation.

The elastomeric butadiene polymers employed in this invention are wellknown in the prior art and many are available commercially. Homoandcopolymers of butadiene with styrenes prepared by organolithiumcatalysis (with or without modifiers such as ethers, amines, etc.) andby sodium catalysts are particularly useful in this invention.Elastomers prepared by free radical catalysis (usually in emulsion) arealso highly useful. Free radical polymerizations are commonly employedfor the preparation of commerical grades of butadieneacrylonitrileelastomers, a type of copolymer found particularly suitable for thisinvention. Excess quantities of emulsifiers and rosin or fatty acidsusually present in elastomers prepared by emulsion polymerization shouldbe removed prior to the process for preparing rigid cyclized productstherefrom.

The elastomeric butadiene copolymers suitable for the purposes of thisinvention will contain at least about 15 mole percent, preferably 30-40mole percent. based on total monomers, of the polymerizable olefinicallyunsaturated monomer. Suitable polymerizable monomers include styrene andsubstituted styrenes such as alpha-methyl styrene, 0-, m-, orpchlorostyrene, the various dibromoand dichlorostyrenes, p-methoxystyrene, the vinyl toluenes such as p-methyl styrene and m-methylstyrene, p-t-butyl styrene, the dimethyl styrenes, etc.; unsaturatednitriles and acrylates such as acrylonitrile, alphamethyl acrylonitrile,ethyl acrylate, butyl acrylate, methyl methacrylate, etc.; vinyl ethers,vinyl ketones, vinyl chloride, alphaand beta-vinyl naphthalenes, etc.The preferred elastomers for use in this invention are the copolymers ofbutadiene and styrene, and butadiene and acrylonitrile.

The term monoolefinic monomers as used in the specification and claimsmeans monomers having only one site of olefinic unsaturation in theirmolecule. The scope of the term includes not only hydrocarbon compoundsbut heterogeneous compounds such as nitriles, ethers, acrylates, ketonesand halogen-containing monomers, e.g., chlorinated. The preferredmonoolefiB 11QI!9H f ar 2-C r qw The preferred organic compounds arehydrocarbons and nitriles.

The elastomeric butadiene coopolymers employed in this invention may berandom, block or of the graft type. The butadiene polymers employed inthis invention should be of such molecular weight that they process wellon conventional rubber equipment. Mooney viscosity values of the rawpolymers (i.e. the curable elastomers) in the 4555 range are preferred.

THE CURING AGENT The curing agent employed in the process of thisinvention is an organic peroxide or mononuclear quinone or halogenatedquinone; generally, such curing agents will be utilized in amounts of0.5 to 10, preferably 1 to 3 parts, per parts of the butadiene polymer.Although the choice of the curing agent is not critical, as a matter ofconvenience it is desirable to utilize organic peroxides or quinoneswhich have a sufficiently high half-life temperature so as to facilitatemixing of the butadiene polymer with the curing agent at elevatedtemperatures without premature crosslinking occurring during the mixingoperation. Desirably, the organic peroxide will have a half-life of atleast 10 minutes at 260F. Suitable examples of such organic peroxidesinclude t-butyl peroxy isobutyrate, di-t-butyl diperthalate, t-butylperbenzoate, dicumyl peroxide, di-t-butyl peroxide, t-butylhydroperoxide, t-methane hydroperoxide, 2,5-dimethyl-2,5 bis(t-butylperoxy) hexane and 2,5-dimethyl-2,5 bis(t-butyl-peroxy)hexyne-3, bis(alpha-tert.-butylperoxy isopropyl) benzene, etc. Thequinone useful for the purposes of the present invention may be amononuclear quinone or halogenated quinone as well as its derivatives.Suitable quinones and halogenated quinones include oand p-benzoquinones,

tetrabromo-p-benzoquinone, and tetrachloro-obenzoquinone, etc. Thepreferred quinone curing agent for the purposes of the present inventionis tetrachlorop-benzoquinone (i.e. chloranil). Use of about one part ofzinc oxide per 100 parts of rubber with the chloranil is recommended inorder to get most effective use of this quinone. The preferred organicperoxide is dicumyl peroxide and particularly preferred isbis-(alpha-tert.-butylperoxy isopropyl) benzene.

THE GRAPHITE FILLER The graphite filler employed for the purposes ofthis invention must be a natural, as distinguished from the synthetic orartificial, type of graphite. Such natural graphite fillers will, forthe purposes of the present invention, be present in the form ofcrystalline flakes or needles or possibly amorphous with the crystallineflake form most preferred and the amorphous form least preferred. Thenatural graphite filler will generally be employed in amounts of about100 to about 800 parts, preferably 200-600 parts, per 100 parts of thebutadiene polymer.

Best results are obtained with maximum filler loadings and for a giventype of natural graphite, the amount of loading of filler with a givenbutadiene polymer will be primarily dependent upon the size of theparticles. Thus, higher loadings can be obtained with the largerparticles, while at low loadings, powders having a particle size rangeof a few microns diameter give the best results. In general, graphitefillers having a particle size distribution in excess (i.e. coarser)than about 90 percent through 200 mesh are undersirable since they aretoo large to provide adequate surface for bonding with the butadienepolymer matrix.

As mentioned above, it is necessary that the graphite filler employed inthe process of this invention be a natural as distinguished from asynthetic or artificial type of graphite. This criticality of thegraphite being of the natural type is dictated by experimental resultsin which it was found that use of synthetic graphites prepared by thehigh temperature pyrolysis of gaseous hydrocarbons, or artificialgraphites prepared by heating mixtures of coke and pitch, result inblistering of the surface of the butadiene polymer upon vulcanizationand/or the subsequent step of cyclization, or products of low strength.

It has also been found that the degree of purity of the natural graphitefiller can also affect the products obtained after vulcanization and/orthe cyclization step. Thus, all other factors being equal, 85 percentpurity graphite results in a product having severe blisters aftervulcanization in contrast to the 98 percent (or higher) pure graphitewhich results in blister-free products. On the other hand, the impurenatural graphite is desirable from an economic point of view since it isconsiderably less expensive than the pure graphite.

It has not been found that it is possible to upgrade impure (i.e.,purity levels of 80-90 percent) graphite by certain treatments to bedescribed hereinbelow; such upgraded graphite will result in productswhich are blister-free and which possess physical properties of the sameorder as those obtained with the use of the pure graphite fillers. Theupgrading of the impure graphite is accomplished by treating the impuregraphite with one or more reagents which are capable of reacting withthe water of crystallization contained in the impure graphite. Thesereagents include silane esters,

e.g., gamma-methacryloxypropyl trimethoxysilane, vinyl triethoxysilane,trimethoxyethoxy vinyl silane, gamme-methacrylpropyl trimethoxy silaneand styrenyl trimethoxy silane; acid anhydrides, e.g., acetic anhydride,maleic anhydride, propionic anhydrode, monochloroacetic anhydride,'andtrichloroacetic anhydride; and metal oxides, e.g., magnesium oxide. zincoxide, barium oxide, calcium oxide, and strontium oxide. etc. Inaddition, it is also possible to use a combination of such reagents,e.g., magnesium oxide and the silane esters, acidic anhydride followedby addition of magnesium oxide, etc.

The upgrading treatment is readily accomplished by contacting 0.5-5parts, per parts of the impure natural graphite, of the reagent with theimpure natural graphite filler at temperatures in the range of F. to300F. for about 20 minutes 3 hours (tumbling of the graphite with thereagent is a convenient method of accomplishing such treatment).Alternatively, the upgrading treatment may be accomplished by simpleadmixture of the impure natural graphite, the reagent and the selectedbutadiene polymer prior to addition of the curing agent and hot millingsuch mixture at elevated temperatures (e.g., 200-300F.) for 2 minutes 1hour.

The first step of the process of this invention involves the mixing ofthe curable elastomeric butadiene polymer with natural graphite filler(and if desired, plasticizers, extender oils, antioxidants, etc.). Whena high proportion of a natural graphite filler is to be employed, it isdesirable to add such a filler to a cement or a solution of the rubber,mixing this cement or solution with the selected filler and therafterremoving the solvent. in case of those elastomers synthesized insolution, such as those prepared with metal alkyl catalysts, it may beeconomically desirable to use the solution of rubber obtained in thesynthesis. Also, in case of elastomers synthesized in emulson, thegraphite and other additives may be added to the synthetic latex priorto coagulation and isolation of the rubber. The preparation of suchpremixes represents a preferred method of preparing rubber-graphiteblends since, because of the lubricity of graphite, mechanical mixing ofthis filler with an elastomer may be difficult. Also, since graphiteparticles do not agglomerate as do carbon blacks, a graphite powder isdispersed relatively easily into a rubber latex or cement.

Use of some plasticizer with the rubber may be desirable from thestandpoint of mixing. However, inert plasticizers such as mineral oilsand esters of saturated acids and alcohols tend to lower the physicalproperties of the cyclized products. A preferred plasticizer is apolybutadiene or butadiene copolymer resin not greater than about 15,000molecular weight and having at least 50 percent of its unsaturation asthe l,2-type. Such plasticizers co-react with the elastomer during thecuring and cyclization steps and actually enhance the physicalproperties of the cyclized composite.

The mixing of the curable elastomeric butadiene polymer with the naturalgraphite filler (and with other desired additives) may be carried outwith conventional rubber blending equipment, e.g., Banburies, extruders,roller mills, etc. The mixing operations may take place at anytemperature; however, prior to adding the curing agent, the compoundshould be cooled to 200F. or lower and a temperature of about 275F.should not be exceeded during the final phase of the mixing process.Mixing temperatures will depend on the particular elastomeric curablebutadiene polymer and the particular curing agent employed, but ingeneral should not exceed 350F. even in the absence of the curing agent.

The admixture of the elastomeric curable butadiene compound and theselected curative is then cured by heating at a temperature sufficientto activate the selected curative, e.g. 275 to 400F., preferably 290 to320F. for a period of time ranging from 5 minutes to 2 hours, preferablyto 40 minutes. It is generally desirable that curing take place in themold of the shape desireed for the final article; mold curing isparticularly suitable where it is not desired to extensively machine thefinal article into its desired shape. When mold curing is employed, itis desirable to utilize sufficient pressure to force the butadienepolymer mixture into the desired shape, e.g., pressures of 400-10,000psi, preferably 500-l,200 psi, are suitable.

After the butadiene polymer has been cured, it is removed from the mold(if a mold is utilized and thereafter cyclized by heating attemperatures in the range of about 330F. to about 700F. for about 2 toabout 40 hours. The reactions which occur during the thermal treatment(heating at a temperature in the range of about 350F. to about 700F.)are primarily noncatalytic in nature, and it is possible to convert thebutadiene polymers employed in this invention to hard, rigid, thermosetmaterials by heat alone (i.e., without previously curing the elastomericbutadiene polymer). The reactions which convert the elastomericbutadiene polymers to rigid thermoset materials are a combination ofring formation and crosslinking. The term cyclization as employed in thedisclosure of this invention denotes a combination of intra-molecularring formation and inter-molecular crosslinking; the term cyclizationemployed in the disclosure of this invention is also synonomous withthermal treatment.

Preferably cyclization is carried out by heating the cured polymer at atemperature of about 350450F. for 20 minutes to 4 hours and thereafterelevating the temperature to 500600F. for a period of time in the rangeof 2 to 36 hours. The cyclization step should take place in the presenceof an inert atmosphere, e.g., nitrogen, argon, helium, etc., or in avacuum, since the presence of oxygen or oxygen-containing gases duringthe cyclization step may adversely affect the surface of BUTADlENEELASTOMERS USED the cyclized butadiene polymer. Since an exothermicreaction is developed during the cyclization step. it may be desirableto carry out this operation in contact with metal plates to absorb theheat generated or in an inert liquid which could be externally heated orcooled in order to control the desired temperature (of course, this heattransfer medium should have a boiling point in excess of thetemperatures employed during the cyclization step).

In particular, it has been found that when relatively thick articlesarebeing cyclized, it is desirable to carry out the cyclization step in aliquid medium such as organic silicones, molten sodium, molten alloys oflead, or certain eutectic salt mixtures. The cyclization step need notbe carried out on the article while it is in the mold, since the curedbutadiene polymer will retain its shape during cyclization. Indeed, itis desirable that the cyclization step not be carried out with thearticle within the mold in order to allow the escape of any materialsvolatile at the cyclization temperature which were present in theoriginal elastomer or which were generated in the curing step.

The cyclized butadiene polymers prepared by the process of thisinvention are easily machined, drilled, and sawed into desired shapes.They have improved impact properties over those of all thermosetplastics, both filled and unfilled, unless the latter contain fibrousfillers. Compression, flexural, and tensile modulii of these uniquehighly filled products are outstanding. Mechanical strength propertiesare good and are unexpectedly high compared to thermoset resinscontaining graphite or other particle fillers. The cyclized butadienepolymers also have a high degree of resistance to aging in air. exposureat elevated temperatures, and corrosive chemicals (such as salts, Brmineral acids, etc.). As such, the cyclized butadiene polymers preparedby the process of this invention may be utilized and indeed give betterperformance in some of those areas in which polyesters, epoxies,phenolics, and other thermoset plastics are usually employed.

The following examples are submitted to illustrate the process of thisinvention. Unless otherwise indicated, all parts are on a weight basisand the temperatures employed throughout are in F.

.22. it EXAMPLE} Listed below in Tables I and I] are the curableelastomeric butadiene polymers and the graphite fillers employed insubsequent Examples 2 and 3.

TABLE I Monomer Microstructurc Mooncy Trademark Name* Co-MonomerSequence Vinyl 7; Cis /r Trans Viscosity Solprene-30l 25-Styrene Random16.7 29.6 53.7 77 Solprene-303 48-Styrene Partial Block 36.2 l7.0 46.845 Solprene-304 IO-Styrene Random 27.] 27.7 45.2 32 Solprene-ZOl NoneHomopolymer 8.3 42.0 49.7 5 Solprene-l204 25-Styrene Random 3L8 26.042.2 52 Solprene-l205 ZS-Styrene Block 9.9 35.2 54.9 47

Paracril-D 44-Acrylonitrile Random 20 20 so Paracril-CJLT39-Acrylonitrilc Random 18 7 1) Paracril-C JS-Acrylonitrilc Random 20 20(to so Purucril-l! 26-Acrylonitrilc Random 20 20 (to so Paracril-BJ26-Acrylonitrile Random 20 20 oil no The Solprcne elastomers wereobtained from the Phillips Petroleum (.ompanyand the Paracrils from theUnitotnl (heunt-al ('ompun) TABLE II NATURAL GRAPHITE FlLLERS USEDSample Name* Type Carbon Particle Size Remarks A-23OU Natural-Flake 99+98% Through 325 Mesh Madagascar, Large Flake Type A-230 Natural-Flake99+ 65% Through 325 Mesh Madagascar, Coarser Grade A'92Natural-Crystalline 98+ 66% Through 325 Mesh Coarse Grade of theCrystallinc Type A-280H Natural-Crystalline 98+ 98% Through 325 MeshCeylon. Needle Type Crystals A-l8 Natural-Crystalline 98+ 83% Through200 Mesh Coarse Grade of the Crystalline Type A-441 Natural-Flake 85 90%Through 325 Mesh Mine Run Madagascar Type A'509F Natural-Amorphous 8590% Through 325 Mesh Mine Run Mexican Type A-Micro 875 Natural-Flake99.9 78% Zero-2 Microns; only Highly Refined and finely 0.4% overMicrons ground Madagascar Type A4084 Artificial 99.8 98% Through 325Mesh Manufactured Products and 8-5033 Artificial 98 99% Through 325 MeshMore Porous Than Naturals Pyrolytic Synthetic 99 Macro as Received MostPerfect Graphite Crystal The A samples were obtained from AsburyGraphite Mills. Inc. the S sample from the Superior Graphite Company.and the pyrolytic grade from the National Carbon Products Company.

EXAMPLE 2 under about 1,000 psi pressure. Portions of the cured 20rubber were then placed in a nitrogen atmosphere in an Elastomericbutadiene polymer blends were preoven, brought to 350F. and thetemperature gradually pared by mixing, on a dual roller mill, theelastomeric raised to 500F. over a period of 2 /2 hours. They werebutadiene polymer (100 parts in each case) and the then baked at 500F.for the indicated number of hours components set forth in Table III.After mixing the and the physical properties of the baked samples (i.e.,components, each rubber blend was vulcanized by 25 theinfusible,cyclized elastomers) are set forth in Table heating at 310F.for 40 minutes in a compression mold IV.

TABLE [I1 Run No. Elastomer Graphite Type Graphite Parts Curutivc &Parts 1 Solprene-SOI None None Dicup"", 1.25 2 Paracril C None NoneDicup. 1.25 3 Paracril CJLT None None Dicup. 1.50 4 Solprene-30l A-230U240 Dicup. 1.25 S Solprene-201 A-230U 216 Dicup. 1.25 6 Solprene-303A-230 320 Dicu'p. 1.25 7 Solprene-303 A-230 240 Dicupv 1.25 8Solprene-303 A-230U 240 Dicup. 1.25 9 Solprene-303 A-230U 180 Dicup.1.25 10 SoIprene-303 A-23OU 216 Dicup. 1.25 11 Solprene-303 A-280H 500""Dicup. 1.25 12 Solprene-303 A-28OH 240 Dicup. 1 25 13 Solprene-303 A-518500"" Dicup. 1.25 14 Solprene-303 A-5l8 600"" Dicup. 1.25 15Solprene-303 A-518 168 Dicup. 1.25

A-280H} 56 A-92 56 16 Solprene-303 A-Micro 875 220 Dicup. 1.25 17Solprene-303 A4084 200 Dicup, 1.25 18 Solprene-303 S-5033 220 Dicup.1.25 19 Solprene-304 A-23OU 216 Dicup, 1.25 20 Solprene-1204 A-230U 240Dicup. 1.25 21 Solprene-1205 A-230U 240 Dicup. 1.25 22 Paracril-B A-230U200 Dicup. 1.25 23 Paracril-B] A-230U 220 Dicup, 1.25 24 Paracril-CA-230U 200 Dicup. 1.25 25 Paracril-C Pyrolytic 240 Dicup, 1.5 26Paracril-D A-230U 200 Dicup. 1.25 27 Paracril-CJLT A-230U 220 Dicup,1.25 28 Paracril-CJLT A-230U 100 Dicup. 1.5 29 Paracril-CJLT A-230U 26(1Chloranil. 4 30 Purified CJLT A-230U 310 Chlnranil, 3

ZnO. 1 31 Paracril C A-230U 240 Chloranil, 3

Paracril CJLT ZnO. 1 32 Paracril C A-280H 240 Chloranil- 3 Paracril CJLTZnO. 1 33 ParacrilC A-92 24o Chloranil,3

Paracril CJLT ZnO. 1 34 Paracril C A-23O 280 Chloranil. 3

Paracril CJLT ZnO. 1 3s ParacrilC"" A-518 168 Chloranil.3

Paracril CJLT A-ZSOH 56 ZnO. 1

A-92 56 36 Paracril BJ A-230U 240 Chloranil. 3

ZnO. 1

""Dicup dicurnyl peroxide 'Tltese mixtures were prepared from cements incontrast to mill mixing employed in the other runs.

"Commercial grade of Paracril CJLT which was purified by washing withmethanol. \acuunt dr tng and milling to remove traces of solvent.

"Blends were 511/ by weight.

TABLE IV Flcxural Strength Flexural Modulus At Rm. Temp., psi I at Rm.Temp., psi

Run Hours Baked at 500F. Hours Baked at 500F. No. 18 24 18 24 9 10,3152.35) 10 l0 11,945 3.4Xl0 ll 12,910 5.71X10 12 11,670 11,285 4.25X103.8X10 l3 7,770 3.9 10 l4 6,810 5.02X10 15 12,905 5.34Xl0 16 14,7504.5)(10 17 8,715 1.32 l0 18 8,965 8,580 1.53Xl0 1.65 l0 l9 10,7952.81X10 20 10,795 2.95X10 21 4,880 22 13,845 2.92Xl0 23 15,595 3.77X1024 15,810 4.16X10 25 10,790 1.36X10 26 13,640 2.59 10 27 18,340 4.85 1028 13,600 2.22 l0 29 19,605 562x10 30 17,590 612x10 31 17,340 19,0104.84Xl0 5.62X10' 32 18.025 188x10 33 16,810 425x10 34 13,925 4.09Xl0" 3518,050 5.l5 10 30 16,530 18,375 4.41X10 4.53 10 The correspondingtensile values for this sample were: Strength 6,765 psi Modulus 5.05 X10" The tensile strength of this sample was 13,270 psi.

' The tensile modulii of these two samples were 5.95 X 10.

It will be noted that when no filler is used in the flexural flexualmodulus obtained was 350,000 psi. By proper compounding with graphitefillers, it was possible to get modulus values well over five millionand in case of nitrile elastomers, a value over six million. Limiteddata on tensile modulii indicate values at least as high ascorresponding flexural values.

When used in like concentration, a more finely divided graphite gavehigher modulus values. Comparing Runs Nos. 7 and 8 using 240 parts ofnatural flake graphite, that with powder of 65 percent through 325 meshgave a baked composite having a flexural modulus of 4.36 X 10, whereaswhen using like graphite but of particle size 98 percent through 325mesh, the higher value of 5.05 X 10 was obtained. However, with thecoarser graphite it was possible to go to a higher filler concentrationand thereby obtain even higher modulus values. For example, when the 65percent through 325 mesh was used in a like compound but in 320 partsper 100 of elastomer (Run 6), a flexural modulus of 5.95 X 10 wasobtained. However, use of graphite of truly micro particle size (Run 16)failed to give as good modulus value as did the corresponding macrogrades. As is well known, the opposite is true in case of carbon blacks.

Although graphite having the more needle type shaped particles, asexemplified by the so-called crystalline grades, gave somewhat poorerresults than the flake type when used in proportions the order of 240parts (Run No. 12 vs. Run No. 8). when using very high proportions ofgraphite filler, the crystalline grade is preferred. For example, whenusing 500 parts of graphite per parts of butadiene-styrene elastomer, itwas possible to obtain a 5.7 X 10 flexural modulus with the crystallinegrade whereas with the flake grade poor physical properties wereobtained.

It may be noted that the two runs with elastomers containing less than20 percent of their unsaturation as the vinyl type (Runs No. 5 and 21)resulted in products of very low flexural strength and modulus valuestoo low to record.

Runs l7, l8 and 25 illustrate the poor results obtained with syntheticgraphites as compared to natural graphites. This is in spite of the factthat the pyrolytic grade (Run 25) is considered the preferred grade foruse in plastics designated for high temperature uses.

EXAMPLE 3 As listed in Table 11, two graphites were employed which had acarbon content of only about 85 percent (samples nos. A-441 and A-509F);the impurities in these samples are primarily clays. When thesegraphites were used as fillers in the butadiene polymers following theprocedure outlined in Example 2, severe blistering occured during thevulcanization and baking steps. Such blistering is believed to ariselargely from the water of crystallization of the clay impurities, butmay also be due to occluded moisture or other volatile products heldwithin the mass of crystals within the particles.

Graphite sample A-44l having a purity of only about 85 percent wascompared to graphite sample A-23OU, a graphite of like crystallinestructure but 99 percent purity, and a sample of A-44l pretreated asdescribed. Composites were prepared in accordance with the procedure setforth in Example 2. Table V indicates the physical properties of thecorresponding composites.

a. The A-44l graphite was pretreated with two parts of acetic anhydrideand heated at F. for two hours. The treated graphite was then aerated atroom temperature overnight to allow any acetic acid and excess anhydrideto evaporate. One part of morpholine was then added to neutralize anyresidual acid.

The results obtained with the purified A-44l graphite approach thoseobtained with the 99 percent grade. This represents a major saving sincethe cost of high purity grade graphite is about 3% times that of the 85percent grade.

EXAMPLE 4 Graphite Used Flexural, PS1 Type Parts Strength Modulus A-230U280 13,875 5.5 X A-230 320 13,850 6.02 X 10 Thus, use of the reactiveliquid plasticizer resulted not only in improved processability, butalso cyclized products of premium properties.

EXAMPLE 5 Although a peroxide curative is preferred in the vulcanizationstep of an all hydrocarbon elastomer, the quinone type is alsoapplicable. 100 parts of Solprene- 303 was blended on a rubber mill with5 parts of zinc oxide, 240 parts of A-230U graphite filler and 3 partsof chloranil. The rubber blend was cured by heating at 295F. forone-half hour and at 310F. for 5% hour. Samples of the cured rubber werethereafter baked for 18 and 24 hours at 500F. and exhibited thefollowing physical properties:

13,495 psi Flexural strength after 18 hrs. at 500F.

14,325 psi Flexural strength after 24 hrs. at 500F 1 2 Flexural modulusafter 18 hrs. at 500F. 4.45 X 10 psi Flexural modulus after 24 hrs. at500F. 4.62 X 10" psi While the above examples illustrate the inventionin great detail, it should be understood that this invention in itsbroadest aspects is not necessarily limited to the specific materials,conditions and procedures shown therein. The present invention islimited only by the claims which follow.

What is claimed is:

1. A high modulus composite prepared by the cyclization undernon-oxidizing conditions, of a substantially emulsifier-free elastomerchosen from polybutadiene and copolymers of butadiene with acrylonitrileor styrene, and having at least 10 percent 1,2-type unsaturation beforecyclization, and containing 100-800 parts by weight of natural graphiteof at least percentpurity per 100 parts of elastomer, said compositebeing cured with an organic peroxide or quinone prior to cyclization.

2. The composite of claim 1 having tensile and flexural moduliiexceeding one million pounds per square inch.

3. The composite of claim 1 wherein the elastomer is a copolymer ofbutadiene and acrylonitrile.

4. The composite of claim 1 wherein the elastomer is a copolymer ofbutadiene and styrene.

5. The composite of claim 1 wherein the graphite consists of the naturalflake or crystalline grade of at least 98 percent purity.

6. The composite of claim 1 wherein the graphite used is of mine-rungrade of at least 85 percent purity which has been pretreated to removewater of crystallization therefrom prior to mixing with the elastomer.

7. The composite of claim 1 wherein the elastomer is prepared byemulsion polymerization.

8. The composite of claim 2 wherein the graphite powder is of suchfineness that at least percent passes through a ZOO-mesh screen.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION lnventofls) ByronM. Vanderbilt It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

30111121211 1, line 6?, "Butt-xiimessr xlonii.sarils" should read MBu'tedie'se edrylonitrile CwT-iumn .3 line 537, "not" sheuld read now iiliqu mx :3, f 7lfijf=if0d should read anhydride deluxe i, lil'fli? 131"desireed" should read desired 3011mm 5, line 21, a ter "utilized." addline- 23, "530 should read 550 Signed and sealed this 17th day of June1975.

C 0112mm (sat) Attest c. l-IARSl-IALL DANN UT C MASON Commissioner ofPatents -;*'teStinrz Officer and Trademarks FORM PC4050 (10-69)UsCoNM-Dc eoszvmpsg

1. A HIGH MODULUS COMPOSITE PREPARED BY THE CYCLIZATION UNDERNON-OXIDIZING CONDITIONS, OF A SUBSTANTIALLY EMULSIFIERFREE ELASTOMERCHOSEN FROM POLYBUTADIENE AND COPOLYMERS OF BUTADIENE WITH ACRYLONITRILEOR STYRENE, AND HAVING AT LEAST 10 PERCENT 1,2-TYPE UNSATURATION BEFORECYCLIZATION, AND CONTAINING 100-800 PARTS BY WEIGHT OF NATURAL GRAPHITEOF AT LEAST 85 PERCENT PURITY PER 100 PARTS OF ELASTOMER, SAID COMPOSITEBEING CURED WITH AN ORGANIC PEROXIDE OR QUINONE PRIOR TO CYCLIZATION. 2.The composite of claim 1 having tensile and flexural modulii exceedingone million pounds per square inch.
 3. The composite of claim 1 whereinthe elastomer is a copolymer of butadiene and acrylonitrile.
 4. Thecomposite of claim 1 wherein the elastomer is a copolymer of butadieneand styrene.
 5. The composite of claim 1 wherein the graphite consistsof the natural flake or crystalline grade of at least 98 percent purity.6. The composite of claim 1 wherein the graphite used is of mine-rungrade of at least 85 percent purity which has been pretreated to removewater of crystallization therefrom prior to mixing with the elastomer.7. The composite of claim 1 wherein the elastomer is prepared byemulsion polymerization.
 8. The composite of claim 2 wherein thegraphite powder is of such fineness that at least 90 percent passesthrough a 200-mesh screen.